1. Field of the Invention
The present invention relates to wireless communications. More particularly, the present invention relates to a Log-Likelihood Ratio (LLR) combining method and apparatus for Hybrid Automatic Repeat Request (HARQ) in a wireless communication system for reducing a number of LLR bits of a previous packet stored for LLR combining.
2. Description of the Related Art
Next generation communication systems support new technologies to secure high quality and high speed communication. A wireless communication system has a high link error rate and limited resources for error correction as compared to its wire link counterpart. Hybrid Automatic Repeat Request (HARQ) is a technique that improves link performance in a resource-constrained wireless communication environment.
The HARQ technique is an error control technique that combines Automatic Repeat Request as an error control technique on a data link layer and channel coding as another error control technique on a physical layer. The HARQ technique reduces a number of retransmissions, thereby increasing system throughput and transmission efficiency. Typically, the HARQ technique is effective when the channel condition is time-varying and thus a modulation scheme of a transmitter is not adaptive to the channel condition.
Two types of HARQ techniques are Chase Combining and Incremental Redundancy. In Chase Combining, the decoder combines the retransmitted packets with an original packet erroneously transmitted in a previous transmission. In Incremental Redundancy, additional redundant information is transmitted in each retransmission to increase a channel coding gain. When retransmission is requested by the receiver the decoder combines previously stored data with retransmitted data before decoding, thereby improving decoding performance. With the application of the HARQ technique, a number of retransmission requests of the receiver decreases, resulting in improvement of the link efficiency.
Therefore, a need exists for an LLR combining method and apparatus for HARQ in a wireless communication system with improved transmission signal estimation and resource utilization.